The use of turbochargers to increase engine performance is well known. Simply put, turbochargers increase the mass of air supplied to an engine, resulting in improved engine performance.
A typical turbocharger comprises a turbine wheel connected to a compressor wheel by a rotatable shaft. Hot engine exhaust gas powers (rotates) the turbine wheel which drives the compressor wheel. The compressor wheel draws in relatively cool ambient air and compresses it before it enters the engine intake manifold.
Compressor wheels operate at very high speeds, often up to 90,000 RPM in large turbochargers used in some heavy duty vehicles and up to 250,000 RPM in automobiles. Over time the compressor wheel can become subject to fatigue failure due to the high speeds or a high cycle (on-off) rate. Replacing the compressor wheel with a new compressor wheel is expensive.
It is known in the industry that shot peening improves the service life of metal components. For example, shot peening of fatigue damaged aluminum parts to extend service life has been practiced in the aerospace industry.
What was not heretofore known was a method of extending the service life of used compressor wheels comprising an inspection step and a renewing step, wherein the inspection step comprises conducting a non-destructive examination of the used compressor wheel to detect cracks larger than those which would fall generally within the compressive stress zone that is generated with peening to identify used compressor wheels that are candidates for renewal, and the renewing step comprises peening to impart compressive residual stresses in those surface regions of the compressor wheel subject to the highest fatigue loadings.